Impact of Sugarcane Cultivation on C Cycling in Southeastern United States Following Conversion from Grazed Pastures

Themes: Sustainability

Keywords: Carbon, Field Data, Soil

Citation

Gomez-Casanovas, N., Blanc-Betes, E., Bernacchi, C.J., Boughton, E.H., Yang, W., Moore, C., Pederson, T.L., Saha, A., DeLucia, E.H. Aug. 28, 2024. “Impact of Sugarcane Cultivation on C Cycling in Southeastern United States Following Conversion From Grazed Pastures.”. FigShare. DOI: 10.6084/m9.figshare.26863441.v1

Overview

Net ecosystem carbon (C) balance (NECB), net ecosystem CO2 exchange, C lost by grazing, fire, and harvest, and other inputs (C from feces in pastures and C from prior land use) for plant cane (PC), first (FRC) and second (SRC) ratoon canes, and improved (IM) and semi-native (SN) pastures. Inputs of C are indicated as negative values, and C outputs as positive values. The NECB represents the net storage (negative values) or loss of C (positive values) at the ecosystem scale, hence, negative NECB indicates that the ecosystem is a net sink of C, and positive values indicate that it is a net source of C. Error bars represent uncertainty in NECB values. PC was defined as sugarcane crop from planting until first harvest (here, from 2/6/2019 to 2/16/2020), FRC as cane crop from first to second harvest (here, from 2/17/2020 to 2/8/2021), and SRC cane as cane crop from second to third harvest (here, from 2/9/2021 to 4/6/2022).

The expansion of sugarcane, a tropical high-yielding feedstock, will likely reshape the Southeastern United States (SE US) bioenergy landscape. However, the sustainability of sugarcane, particularly as it displaces grazed pastures, is highly uncertain. Here, we investigated how pasture conversion to sugarcane in subtropical Florida impacts net ecosystem CO2 exchange (NEE) and net ecosystem carbon (C) balance (NECB). Measurements were made over three full growth cycles (> 3 years) in sugarcane—plant cane, PC; first ratoon cane, FRC; second ratoon cane, SRC—and in improved (IM) and semi-native (SN) pastures, which make up ca. 37% of agricultural land in the region. Immediately following conversion, PC was a stronger net source of CO2 than pastures, indicating the importance of CO2 losses related to land disturbance. Sugarcane, however, shifted to a strong net sink of CO2 after first regrowth, and overall sugarcane was a stronger net CO2 sink than pastures. Both stand age and low water availability during cane emergence and tillering substantially decreased its potential gross CO2 uptake. Accounting for all C gains and removals (i.e., NECB), greater frequency of burn events and repeated harvest increased removals and overall made sugarcane a stronger C source relative to pastures despite substantial C inputs from the previous land use and a stronger CO2 sink strength. Time since conversion substantially reduced C losses from sugarcane, and the NECB of SRC was similar to that of IM pasture but lower than that of SN pasture, indicating a rapid shift in the NECB of cane. We conclude that the C-balance implications following conversion will depend on the proportion of IM versus SN pastures converted to sugarcane. Furthermore, our findings suggest that no-burn harvest management strategies will be critical to the development of a sustainable bioenergy landscape in SE US.

Data

Data includes:

  • CO2 fluxes (NEE, GPP)
  • Biomet variables (meteorological, soil)

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